Integration of Aerial-Relay-Based Network With Terrestrial Network Towards B5G/6G Evolution.

Aimed at boosting spectrum utilization towards B5G/6G evolution, this paper studies an overlying network that is built by using "dummy" aerial relays and shares the frequency band with a primary network, where the low-cost relays without using sophisticated transmit beamforming generate interference to the primary network. The main objectives are, by using collaborative transmitter precoding, i) to increase Signal-to-Leakage Ratio (SLR) which is the ratio of signal power at the intended receiver to interference power at an unintended receiver, and ii) to reduce the overlying network's total transmit power. A performance trade-off framework based on robust optimization is proposed to balance these two contradicting objectives, with consideration of the relays' asynchronicity and channel measurement errors. It is found that the relays' amplification is a sensitive parameter that can be tuned together with the transmitter precoder in optimization. To overcome the problem of unknown uncertainty set in the max-min optimization, a practical technique based on multiple measurements, semi-analytical robust design, is proposed and tested. Performance evaluation results suggest the proposed overlying network is promising toward the two objectives.